Ngueleu, S.K., Al-Raoush, R.I., Shafieiyoun, S., Rezanezhad, F., Van Cappellen, P., 2019. Biodegradation kinetics of benzene and naphthalene in the vadose and saturated zones of a (semi)-arid saline coastal soil environment. Geofluids 2019, 8124716.

https://doi.org/10.1155/2019/8124716 Biodegradation is a key process for the remediation of sites contaminated by petroleum hydrocarbons (PHCs), but this process is not well known for the (semi)-arid coastal environments where saline conditions and continuous water level fluctuations are common. This study differs from the limited previous studies on the biodegradation of PHCs in Qatari coastal soils mainly by its findings on the biodegradation kinetics of the selected PHCs of benzene and naphthalene by indigenous bacteria. Soil samples were collected above, across, and below the groundwater table at the eastern coast of Qatar within a depth of 0 to - 40 cm. Environmental conditions combining low oxygen and high sulfate concentrations were considered in this study which could favor either or both aerobic and anaerobic bacteria including sulfate-reducing bacteria (SRB). The consideration of SRB was motivated by previously reported high sulfate concentrations in Qatari soil and groundwater. Low- and high-salinity conditions were applied in the experiments, and the results showed the sorption of the two PHCs on the soil samples. Sorption was dominant for naphthalene whereas the biodegradation process contributed the most for the removal of benzene from water. Losses of nitrate observed in the biodegradation experiments were attributed to the activity of nitrate-reducing bacteria (NRB). The results suggested that aerobic, NRB, and most likely SRB biodegraded the two PHCs, where the combined contribution of sorption and biodegradation in biotic microcosms led to considerable concentration losses of the two PHCs in the aqueous phase (31 to 58% after 21 to 35 days). Although benzene was degraded faster than naphthalene, the -3 -2 biodegradation of these two PHCs was in general very slow with rate coefficients in the order of 10 to 10 -1 day and the applied kinetic models fitted the experimental results very well. It is relevant to mention that these rate coefficients are the contribution from all the microbial groups in the soil and not from just one.

Nguyen, T.B., Topçuoğlu, B.D., Holden, J.F., LaRowe, D.E., Lang, S.Q., 2020. Lower hydrogen flux leads to larger carbon isotopic fractionation of methane and biomarkers during hydrogenotrophic methanogenesis. Geochimica et Cosmochimica Acta 271, 212-226.

http://www.sciencedirect.com/science/article/pii/S0016703719307136 The isotopic composition of lipid biomarkers and biomass in sedimentary environments are widely used to infer microbial metabolisms and constrain carbon cycling processes. It has been observed that metabolic energy availability in the form of H impacts the stable carbon isotopes of CH during hydrogenotrophic 2 4 methanogenesis, but it is unknown whether this relationship extends to lipids and amino acids. Since lipids and amino acids are long-lived, they can be used to reconstruct past conditions over geologic timescales. Therefore, the controls on their isotopic signatures are important to constrain to better interpret past environments. In this study, the isotopic distributions of carbon metabolized and reduced by the hyperthermophile Methanocaldococcus jannaschii were quantified following growth at 82 °C in a chemostat with high (80- 83 µM) and low (15-27 µM) H concentrations. As has been shown previously, the stable carbon isotope 2 fractionation factors for CH were >15‰ larger in low H experiments than in high H experiments. Lipid 4 2 2 biomarkers and amino acids were similarly impacted with approximately 10‰ larger fractionation factors und er low H conditions. The increase in fractionation factors can be related to the lower availability of 2 thermodynamic energy, suggesting that even larger fractionation factors would be observed in methanogens living close to their threshold energy needs, as they do in most environments. The resulting isotopic signatures of long- lived lipid biomarkers synthesized by hydrogenotrophic methanogens may become as 'superlight' as those synthesized by archaea carrying out the anaerobic oxidation of methane. These results help to describe the underlying mechanisms that determine the isotopic composition of long-lived biomarkers and provide constraints for interpreting these signatures in the environment.

Ni, M., Li, S., 2020. Optical properties as tracers of riverine dissolved organic matter biodegradation in a headwater tributary of the Yangtze. Journal of Hydrology 582, 124497.